Semiconductor laser device

Abstract

The semiconductor laser device includes: an activation layer having at least one first quantum dot layer and at least one second quantum dot layer having a longer emission wavelength than the first quantum dot layer. The gain spectrum of the active layer has the maximum values at the first wavelength and the second wavelength longer than the first wavelength corresponding to the emission wavelength of the first quantum dot layer and the emission wavelength of the second quantum dot layer, respectively. The maximum value of the gain spectrum at the first wavelength is defined as the first maximum value, and the maximum value of the gain spectrum at the second wavelength is defined as the second maximum value. The first maximum value is larger than the second maximum value.

What is claimed is: 
     
       1. A semiconductor laser device comprising:
 an active layer having a structure including one or more first quantum dot layers and one or more second quantum dot layers having an emission wavelength longer than that of the first quantum dot layer, wherein: 
 a gain spectrum of the active layer has maximum values at a first wavelength and a second wavelength longer than the first wavelength, corresponding to the emission wavelength of the first quantum dot layer and the emission wavelength of the second quantum dot layer; 
 the maximum value of the gain spectrum at the first wavelength is defined as a first maximum value; 
 the maximum value of the gain spectrum at the second wavelength is defined as a second maximum value; 
 the first maximum value is larger than the second maximum value; 
 a numerical number of the first quantum dot layers in the active layer is larger than a numerical number of the second quantum dot layers; 
 a wavelength between the first wavelength and the second wavelength when the gain spectrum takes a minimum value is defined as a third wavelength; 
 a temperature at which an intensity of the gain spectrum is maximum is defined as T p ; 
 the second wavelength at a temperature T L  lower than the temperature T p , the third wavelength at the temperature T p , and the first wavelength at a temperature T H  higher than the temperature T p  are equal; 
 the numerical number of the first quantum dot layers is defined as X; 
 the numerical number of the second quantum dot layers is defined as Y; 
 the first maximum value at the temperature T p  is defined as G MAX1  (T p ); 
 the second maximum value at the temperature T p  is defined as G MAX2  (T p ); 
 the second maximum value at the temperature T L  is defined as G MAX2  (T L ); 
 the first maximum value at the temperature T H  is defined as G MAX1  (T H ); and 
 X is an integer closest to {G MAX2 (T L ) / G MAX2  (T p )} ·{G MAX1 (T p ) / G MAX1  (T H )} ·Y. 
 
     
     
       2. The semiconductor laser device according to  claim 1 , wherein:
 a density of quantum dots in the first quantum dot layer is larger than a density of quantum dots in the second quantum dot layer. 
 
     
     
       3. The semiconductor laser device according to  claim 1 , wherein:
 the second maximum value at the temperature T L  is closer to the minimum value at the temperature T p  than the second maximum value at the temperature T p ; and 
 the first maximum value at the temperature T H  is closer to the minimum value at the temperature T p  than the first maximum value at the temperature T p . 
 
     
     
       4. The semiconductor laser device according to  claim 1 , further comprising:
 a wavelength selection unit for selecting an operating wavelength of the active layer, wherein: 
 the wavelength selection unit selects the operating wavelength to be longer than the first wavelength at the temperature T p  and shorter than the second wavelength at the temperature T p . 
 
     
     
       5. The semiconductor laser device according to  claim 4 , wherein:
 the wavelength selection unit selects the operating wavelength to be closer to the third wavelength at the temperature T p  than the first wavelength at the temperature T p , and to be closer to the third wavelength at the temperature T p  than the second wavelength at the temperature T p . 
 
     
     
       6. The semiconductor laser device according to  claim 4 , wherein:
 the wavelength selection unit selects the operating wavelength so as to oscillate the active layer in a single mode. 
 
     
     
       7. The semiconductor laser device according to  claim 1 , wherein
 the second maximum value at the temperature T L , the minimum value at the temperature T p , and the first maximum value at the temperature T H  are equal to each other. 
 
     
     
       8. The semiconductor laser device according to  claim 1 , wherein:
 the active layer has a characteristic that an intensity of the gain spectrum decreases and an emission wavelength shifts to a short wavelength side when a temperature of the active layer becomes lower than the temperature T p , and the intensity of the gain spectrum decreases and the emission wavelength shifts to a long wavelength side when the temperature of the active layer becomes higher than the temperature T p . 
 
     
     
       9. The semiconductor laser device according to  claim 1 , wherein:
 the active layer includes a p-type impurity. 
 
     
     
       10. A semiconductor laser device comprising:
 a light source that generates a laser light, wherein: 
 the light source includes an active layer having one or more first quantum dot layers with first quantum dots and one or more second quantum dot layers with second quantum dots; 
 a size of each of the second quantum dots is larger than a size of each of the first quantum dots; 
 a gain spectrum of the active layer has maximum values at a first wavelength and a second wavelength longer than the first wavelength, corresponding to the emission wavelength of the first quantum dot layer and the emission wavelength of the second quantum dot layer; 
 the maximum value of the gain spectrum at the first wavelength is defined as a first maximum value; 
 the maximum value of the gain spectrum at the second wavelength is defined as a second maximum value; 
 the first maximum value is larger than the second maximum value; 
 a numerical number of the first quantum dot layers is larger than a numerical number of the second quantum dot layers; 
 a wavelength between the first wavelength and the second wavelength when the gain spectrum takes a minimum value is defined as a third wavelength; 
 a temperature at which an intensity of the gain spectrum is maximum is defined as T p ; 
 the second wavelength at a temperature T L  lower than the temperature T p , the third wavelength at the temperature T p , and the first wavelength at a temperature T H  higher than the temperature T p  are equal; 
 the numerical number of the first quantum dot layers is defined as X; 
 the numerical number of the second quantum dot layers is defined as Y; 
 the first maximum value at the temperature T p  is defined as G MAX1  (T p ); 
 the second maximum value at the temperature T p  is defined as G MAX2  (T p ); 
 the second maximum value at the temperature T L  is defined as G MAX2  (T L ); 
 the first maximum value at the temperature T H  is defined as G MAX1  (T H ); and 
 X is an integer closest to {G MAX2 (T L ) / G MAX2  (T p )} ·{G MAX1 (T p ) / G MAX1  (T H )} ·Y. 
 
     
     
       11. A semiconductor laser device comprising:
 a light source that generates a laser light, wherein: 
 the light source includes an active layer having a first quantum dot layer with first quantum dots and a second quantum dot layer with second quantum dots; 
 a size of each of the second quantum dots is larger than a size of each of the first quantum dots; 
 a density of the first quantum dots in the first quantum dot layer is higher than a density of the second quantum dots in the second quantum dot layer; 
 a gain spectrum of the active layer has maximum values at a first wavelength and a second wavelength longer than the first wavelength, corresponding to the emission wavelength of the first quantum dot layer and the emission wavelength of the second quantum dot layer; 
 the maximum value of the gain spectrum at the first wavelength is defined as a first maximum value; 
 the maximum value of the gain spectrum at the second wavelength is defined as a second maximum value; 
 the first maximum value is larger than the second maximum value; 
 a numerical number of the first quantum dot layers in the active layer is larger than a numerical number of the second quantum dot layers; 
 a wavelength between the first wavelength and the second wavelength when the gain spectrum takes a minimum value is defined as a third wavelength; 
 a temperature at which an intensity of the gain spectrum is maximum is defined as T p ; 
 the second wavelength at a temperature T L  lower than the temperature T p , the third wavelength at the temperature T p , and the first wavelength at a temperature T H  higher than the temperature T p  are equal; 
 the numerical number of the first quantum dot layers is defined as X; 
 the numerical number of the second quantum dot layers is defined as Y; 
 the first maximum value at the temperature T p  is defined as G MAX1  (T p ); 
 the second maximum value at the temperature T p  is defined as G MAX2  (T p ); 
 the second maximum value at the temperature T L  is defined as G MAX2  (T L ); 
 the first maximum value at the temperature T H  is defined as G MAX1  (T H ); and 
 X is an integer closest to {G MAX2 (T L ) / G MAX2  (T p )} ·{G MAX1 (T p ) / G MAX1  (T H )} ·Y.